Overview of PCB Assembly Process
Considering our attachment to technology, we can assume that many of us are aware of the importance of circuit boards. They provide the basic internal structure for our appliances to function. Circuit boards are conduits for harnessing electricity and using it to drive electrical products.
Furthermore, circuit boards, too, have undergone revolutionary changes to cope with our evolving technology. While technology was designed to offer convenience in the past, today's technology is more focused on combining convenience, long-term reliability, and user-friendliness. This complex combination requires electrical components that can be utilized for limited space applications while simultaneously allowing for enhanced functionality and tolerance to wear and tear.
As a result, electrical products are designed using printed circuit boards which are far superior to their traditional counterparts. But, how are they made? Is there a process to manufacture printed circuit boards?
As it turns out, there's a process for manufacturing PCBs, referred to as the PCB assembly process. In this article, will walk you through a brief overview of the PCB assembly process.
Printed Circuit Board Assembly
The PCB assembly process refers to the steps used to build fully functional printed circuit boards. Such circuit boards with their components mounted to the substrate are called assembled PCBs. The exact term for the fabrication process is printed circuit board assembly or PCBA.
So, what are the steps for printed circuit board assembly?
PCB Assembly Process Steps
Printed circuit boards are manufactured using steps that are typically standard in all manufacturing companies. Although, before getting down to fabrication, companies do need to perform a design for manufacturability or DFM check. This involves studying the design, design notes, and specific application requirements placed in the client order.
Consequently, the DFM check helps in identifying any structural flaws or potential problems so that design engineers do not get blindsided during the fabrication process. After performing the initial check, the actual steps of the PCB assembly process are followed:
1. Solder Paste Stenciling
The first step in any PCB assembly process is to apply solder paste to the substrate so components can be soldered. The paste is a grayish substance composed of grains of metal called solder. The general composition of the tiny metals is a variable ratio of tin, silver, and copper. Solder is mixed with a flux – a chemical designed to aid the solder in melting and bonding the substrate – to form the solder paste.
In a process similar to printing, the solder paste is applied to all areas of the board that require soldering. In professional manufacturing companies, such as Hemeixin Electronics, the printed circuit board assembly uses a solder screen or mechanical fixture for precise and automated application of the paste to the circuit board.
2. Pick and Place
After the solder paste has been applied, a machine places components onto the circuit board, which are to be soldered in the next step of the printed circuit board assembly. The components can either be surface mount devices or through-hole components. For ease of understanding and the component’s popularity in modern markets, we will be assuming the components are SMDs or surface mount devices.
A machine with different components in reels "picks up" the substrate and moves it to the "pick and place" station. Here, the components are either directly placed or with drops of glue onto the circuit board. The tension between the solder paste and the components helps keep them in place until soldering.
An important step in the PCB assembly process is when the components are soldered to the substrate. These days, the process used for soldering surface mounting technology is "reflow soldering." It is faster and more convenient than other soldering methods, such as wave soldering for through-hole components, which is obsolete when manufacturing double-sided printed circuit boards.
A conveyor belt moves the PCB assembly from the “pick and place” station and directs it to a reflow oven. It has a series of heaters that melt the solder in the paste. The melted solder is then progressively cooled with the help of a series of cooler heaters which solidify the solder.
As a result, the components perfectly adhere to the board and do not fall off when the printed circuit board is subjected to stress or erratic movement.
As the printed circuit board assembly progresses, a series of inspective steps are taken to ensure the final assembly does not have any misaligned components, errors in connections, and shorts.
Common inspection checks include the following methods:
• X-Ray Inspection for complex or multilayered printed circuit boards
• Manual Checks for small batches to increase in-person visual inspection of the printed circuit boards.
• Automatic Optical Inspection with the help of an AOI machine is the best inspection method for large and small batches. Leading manufacturers, such as Hemeixin Electronics, use AOI technology to ensure the best quality control regulations for their products.
Companies are generally moving toward automated inspection processes in which machines can detect weak joints, weak finishes, incomplete solder paste stenciling, misplaced or wrongly-placed components. This has further simplified the PCB fabrication process.
PCBs not meeting the company standards are removed and sent back for reworking. After the inspection is carried out, the PCB assembly process can move onto the final step, the functional test.
5. Functional Test
All printed circuit board assembly boards cleared in the inspection check are finally tested for functionality. This is the final inspection and the last step of the PCB assembly process, the functional test.
The functional test simulates the application design for which the PCB is required, and the printed circuit boards are required to operate. Testers continue to monitor the function of all printed circuit boards in the functional test.
Characteristics that are measured include voltage, signal output, current output, and fluctuations and hit peaks outside the predetermined range. Printed circuit boards that fail the final step are sent back, scrapped, or recycled depending on the company policies.
The functional test establishes the success and failure of the PCBs in printed circuit board assembly and is a decisive step in the PCB assembly process. As a result, make sure to only buy printed circuit boards from authorized professional manufacturers such as Hemeixin Electronics, who subject their PCBs to rigorous testing and quality control measures to ensure customer satisfaction!